A legendary trio is a term used to describe a group of three closely-related legendary Pokémon. Legendary trios can be subdivided into two tiers, normal trios and mascot trios. Normal trios, which are always the first legendaries that appear in any Pokédex order, are allowed into the many Battle Towers and other battle facilities. They are also the only Pokémon with base stat totals of 580, besides the legendary musketeers. The mascot trios, whose name comes from the fact that all of them are version mascots, are not allowed in the Battle Tower, and are found close to the end of the Pokédex in the generation of their release.

Five of the eight trios share at least one type, and the members of a legendary trio will also commonly share Ability and base stat total (the kami, weather, and Tao trios being the only trios not doing so). All of the trios have a master who created them according to myth and/or is somehow able to exert control over them, though oftentimes these masters are not introduced until a later generation, or revealed to be the master until a third version.